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<p class="MsoNormal">Dear Ivo,</p>
<p class="MsoNormal">I�m not sure there is a generic solution; following your example Mn3O4 & Fe3O4 each have two different metal atom sites each with different multiplicities in a spinel structure. Since the script is made up of python statements, you could
just tailor the math to fit your specific problem & calculate numbers of FUs you want.</p>
<p class="MsoNormal">Bob</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Sent from <a href="https://go.microsoft.com/fwlink/?LinkId=550986">
Mail</a> for Windows 10</p>
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<p class="MsoNormal" style="border:none;padding:0in"><b>From: </b><a href="mailto:gsas-ii@aps.anl.gov">Ivo Alxneit via GSAS-II</a><br>
<b>Sent: </b>Monday, April 26, 2021 6:30 AM<br>
<b>To: </b><a href="mailto:gsas-ii@aps.anl.gov">gsas-ii@aps.anl.gov</a><br>
<b>Subject: </b>[GSAS-II] Extract number of formula units per unit cell</p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt">Dear all<br>
<br>
I am a chemist that uses xrd-powder diffraction to follow the course of<br>
reactions. Therefore, mass-fractions or number of atoms per unit cell<br>
are not useful to me. I deal with mol fractions of formula units (FU).<br>
To convert from the unit cell related values to FU related values I need<br>
to know the number of FUs per unit cell (Z). How can I calculate this<br>
based solely on the information stored in a gsas-II project (I want to<br>
use scriptable to automate the task).<br>
<br>
<br>
So far I seem to have a solution but I am not sure if it is really correct:<br>
<br>
For each phase, the greatest common divisor (GCD) of the site<br>
multiplicity of all atoms corresponds to Z. As example LaFeO3 (Pnma):<br>
La 4<br>
Fe 4<br>
O1 8<br>
O2 4<br>
Formula per unit cell: La4Fe4O12<br>
GCD=4 -> FU=LaFeO3<br>
<br>
This also gives the correct FU for solid solutions like Ce0.1Ce0.9O2.<br>
<br>
But there are cases where more than one atom form the basis as e.g.<br>
graphite(P63/mmc):<br>
C1 2<br>
C2 2<br>
Formulat per unit cell: C4<br>
GCD=2 -> FU=C2<br>
Here I miss the factor 2 due to the 2-atom basis. How do I identify a<br>
n-atom basis? I assume that in this case I would find for each atom n<br>
sets that have the identical multiplicity. In the case of the LaFeO3<br>
example above a second set with La/4, Fe/4, O1/8, O2/4 would have to be<br>
present.<br>
<br>
So the question: Is my solution generic and correct?<br>
<br>
Thanks for any help / suggestions<br>
<br>
-- <br>
Dr. Ivo Alxneit<br>
Applied Catalysis and Spectroscopy Group<br>
Bioenergy and Catalysis Laboratory phone: +41 56 310 4092<br>
Paul Scherrer Institute fax: +41 56 310 2688<br>
CH-5232 Villigen gnupg key: 0x515E30C7<br>
Switzerland<br>
<a href="https://www.psi.ch/acs/">https://www.psi.ch/acs/</a><o:p></o:p></p>
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